docs: add CLI help

README.md

docs/cmd/tk.md

docs/cmd/tk_check.md

docs/cmd/tk_create.md

docs/cmd/tk_create_kustomization.md

docs/cmd/tk_create_source.md

docs/cmd/tk_create_source_git.md

docs/cmd/tk_delete.md

docs/cmd/tk_delete_kustomization.md

docs/cmd/tk_delete_source.md

docs/cmd/tk_delete_source_git.md

docs/cmd/tk_export.md

docs/cmd/tk_export_kustomization.md

docs/cmd/tk_export_source.md

docs/cmd/tk_export_source_git.md

docs/cmd/tk_get.md

docs/cmd/tk_get_kustomizations.md

docs/cmd/tk_get_sources.md

docs/cmd/tk_get_sources_git.md

docs/cmd/tk_install.md